Math disadvantage, how to calculate it?

[Toby]

Supose you donnot know that French roulette has 2,7% over the player and you start playing 6 numbers.

When you have played 1000 spins you are losing 10% of the total wagged(600).

After 2000 spins played you are 8% down(960).

At spin 10k you are 5% down(3000)

At 50k you are 2,7% down(8100)

We finally reach the -2,7% at 50k.

Supose the oposite, we play 6 or 20 numbers and we are 7 to 10% up most of the time until we drop to -2,7%

Is there a way to get the -2,7% from a start of +10%?

Another scenario, supose you don´t know but a wheel section is not hitting because it has a problem. You, by chance, are not playing the section, you start winning.
How do you calculate the real advantage you have when you do not play the section?